Composite sandwich constructions may be strengthened by placing structural reinforcement inside a core that is bonded between two facesheets. The core reinforcement may include structural elements that define load paths for transferring compressive, tensile and shear loads between the facesheets. The performance of the composite sandwich is dependent in part upon the type of core reinforcement and the quality of the bonds between the core and the facesheets. Common materials used in the core may include rigid plastic foam and honeycomb. While honeycomb cores exhibit good structural efficiency, they may subjected to higher core-to-facesheet loading in some applications, such as long duration space flights where a differential pressure may develop between the core and the surrounding environment.
Unreinforced closed cell rigid foam cores may exhibit reduced structural efficiency when subjected to moisture and to higher temperatures, or extreme low temperatures in space.
The problems associated with the sandwich constructions discussed above have been partially solved by the introduction of so-called X-COR structural cores which comprise a light-weight, closed cell polymethacrylimide (PMI) foam reinforced with small diameter, poltruded carbon fiber/epoxy pins arranged in a tetragonal truss network. The X-COR pins extend beyond the foam core and are embedded in the facesheets. A variation of X-COR is disclosed in U.S. Pat. No. 6,291,049 issued Sep. 18, 2001, in which the ends of the pins are bent so as to lie flat against facesheets to which the core is bonded.
The truss networks mentioned above that employ carbon fiber/epoxy pins may not provide adequate performance in some aerospace applications. Accordingly, there is a need for a composite structure having a reinforced core that is suitable for demanding aerospace applications in which superior bond strength between the facesheets and core is required. Embodiments of the disclosure are intended to satisfy this need.